Microbiology Fundamentals: Cells, Pathogens, and Immunity

Posted on Jun 22, 2025 in Biology

General Microbiology Fundamentals

• Prokaryotic vs. Eukaryotic Cells

  • Prokaryotic: No nucleus (e.g., Bacteria, Archaea)

  • Eukaryotic: Possess a nucleus (e.g., Protists, Fungi, Plants, Animals)

• Unicellular vs. Multicellular Organisms

  Bacteria and Protists are unicellular; Fungi can be unicellular or multicellular; Plants and Animals are multicellular.

• Modes of Nutrition

  • Autotrophs: Produce their own food (e.g., plants)

  • Heterotrophs: Consume other organisms (e.g., animals)

  • Decomposers: Break down dead organic matter (e.g., fungi)

• Key Discoveries in Microbiology

  Microscopes enabled the discovery of microbes. DNA analysis led to the classification of life into three domains: Bacteria, Archaea, and Eukarya.

• Dichotomous Keys for Identification

  A step-by-step tool used to identify organisms by answering a series of yes/no questions.

Bacteria vs. Archaea: Key Differences

• Bacterial Shapes

  Round: Coccus; Rod: Bacillus; Spiral: Spirillum

• Bacterial Groupings

  Diplo: Pairs; Strepto: Chains; Staphylo: Clusters

• Beneficial Roles of Bacteria

  Aid in food digestion, produce dairy products, and are used in bioremediation (e.g., cleaning oil spills).

• Harmful Bacteria and Diseases

  Can cause diseases such as strep throat, food poisoning, and various infections.

• Understanding Antibiotic Resistance

  Occurs when bacteria evolve to survive antibiotic treatments, leading to stronger strains. Prevent by using medications properly.

Viruses: Structure and Replication

• Are Viruses Alive?

  Viruses are not considered living organisms as they lack cellular structure and cannot grow or reproduce independently.

• Viral Components

  Composed of a protein shell (capsid), genetic material (DNA or RNA), sometimes a fatty outer coat (envelope), and spikes for attaching to host cells.

• Lytic Cycle

  The virus takes over the host cell, replicates its components, and then causes the cell to burst, releasing new viruses.

• Lysogenic Cycle

  The viral DNA integrates into the host cell’s DNA, remaining dormant before potentially activating and entering the lytic cycle.

Vaccines and the Immune System

• First Line of Defense

  Physical and chemical barriers that block pathogens (e.g., skin, mucous membranes).

• Second Line of Defense

  Non-specific responses that rapidly fight invaders (e.g., inflammation, fever, white blood cells).

• Third Line of Defense

  Specific responses targeting particular pathogens, involving antibodies and specialized immune cells.

• What are Antibodies?

  Proteins produced by the immune system that bind to specific pathogens to neutralize or mark them for destruction.

• How Vaccines Work

  Introduce a safe, weakened, or inactive form of a pathogen to train the immune system to recognize and fight future infections.

• Types of Immunity

  • Active Immunity: The body produces its own antibodies (e.g., after infection or vaccination).

  • Passive Immunity: Antibodies are received from an external source (e.g., maternal antibodies, antitoxins).

Protists: Diverse Eukaryotic Microbes

• Categories of Protists

  • Animal-like: (e.g., Amoeba)

  • Plant-like: (e.g., Euglena, Algae)

  • Fungus-like: (e.g., Slime Molds)

• Protist Locomotion

  Utilize cilia (tiny hair-like structures), flagella (tail-like structures), pseudopodia (false feet), or are non-motile (floating).

• Ecological Roles of Protists

  Produce oxygen, serve as a food source for aquatic organisms, and some cause diseases (e.g., malaria).

Fungi: Characteristics and Importance

• Fungi vs. Plants: Key Distinctions

  • Fungi are heterotrophic (absorb nutrients), while plants are autotrophic (produce their own food).

  • Fungi cell walls contain chitin; plant cell walls contain cellulose.

• Anatomy of a Mushroom

  Includes the cap, stalk, gills (produce spores), hyphae (thread-like structures), mycelium (a network of hyphae), and sporangia (spore-producing structures).

• Fungal Relationships

  • Mutualism: Both organisms benefit (e.g., lichens).

  • Parasitism: The fungus harms the host (e.g., athlete’s foot).

Microorganism Summary Table

Additional Microbiology Insights

• Archaea thrive in extreme environments like hot springs and salt lakes; their cell walls lack peptidoglycan.

• Bacteria are beneficial in food production (e.g., cheese, yogurt) and environmental remediation (e.g., oil spill cleanup).

• Antibiotic resistance occurs when bacteria survive drug treatments and proliferate.

• Viruses are non-living entities that reproduce by utilizing host cells.

• The Lytic Cycle is rapid and destroys host cells. The Lysogenic Cycle involves viral DNA integrating into host DNA, remaining dormant.

• Immunity Lines of Defense:

  • First Line: Skin, mucous membranes.

  • Second Line: White blood cells, fever, inflammation.

  • Third Line: Antibodies produced by B cells.

• Vaccines prepare the immune system using weakened or inactivated forms of pathogens.

• Protist Characteristics:

  • Locomotion via cilia, flagella, or pseudopods.

  • Some cause diseases, such as malaria.

• Fungi Characteristics:

  • Primary decomposers.

  • Reproduce primarily through spores.

  • Some species produce antibiotics (e.g., penicillin).